The present invention relates to a method and apparatus for bending glass sheets and particularly those that are bent by a method involving conveying glass sheets into a bending station where each glass sheet is delivered at its deformation temperature for bending. After bending, a ring-like member supports the glass sheet for movement from the bending station through a cooling station. Tempering medium, most usually in the form of pressurized blasts of air, is imparted against the opposite surfaces of the glass sheet at the cooling station at a rate sufficient to cool the heated, bent glass sheet and impart at least a partial temper thereto. The bent, tempered glass sheet is then transferred onto a removal conveyor.
In the past, prior art transfer systems limited the speed at which a bending and tempering operation could be performed, because the transfer step was a bottleneck that restricted the rate at which glass sheets could be processed because of the need to unload a bent, tempered glass sheet from the ring-like member before the ring-like member could return to the shaping station to receive a succeeding glass sheet or glass sheet set at the shaping station. Other prior art transfer systems that reduced the duration of the bottleneck tended to cause the bent, tempered glass sheets to become distorted or develop surface mars or breakage due to the nature of the transfer operation in various types of prior art higher speed transfer systems.
Since the automotive industry has been required in recent years to develop automobiles that reduce their fuel consumption, it has become necessary to bend and temper thinner glass sheets than those found suitable in the past. The present invention relates to the treatment of relatively thin glass sheets, particularly those having a nominal thickness of 1/8 inch (3.2 millimeters) or less. Thinner glass sheets sag more readily than thicker glass sheets at any given elevated temperature above the glass deformation temperature. Hence, it is more difficult to control the shape imparted to thinner glass sheets, and in recent years the shaping of thinner glass sheets has incorporated the use of vacuum molds having lower apertured walls enclosing a chamber through which suction is applied to hold a heat-softened glass sheet by vacuum against the downwardly shaping surface of a shaping mold to control its sag during the shaping operation.
Bent glass sheets are widely used as side windows or rear windows in vehicles such as automobiles or the like in positions where tempered glass sheets are permitted. To be suitable for such application, flat glass sheets must be shaped to precisely defined curvatures dictated by the shape and outline of the frame defining the window openings into which the glass side windows and rear windows are installed. It is also important that the side windows meet stringent optical requirements and that the windows be free of optical defects that would interfere with the clear viewing therethrough, particularly in their viewing area.
During their fabrication, glass sheets intended for use as shaped windows in vehicles are subjected to thermal treatment to temper as well as to bend the glass sheets. Tempering increases the resistance of the shaped windows to damage resulting from impact. In addition to increasing the resistance of the glass sheet to breakage, tempering also causes the glass sheet to fracture into relatively small, relatively smoothly surfaced fragments that are relatively safe compared to the relatively large, jagged fragments that result from the more frequent breakage of untempered glass.
The commerical production of bent glass sheets for such purposes commonly includes heating flat glass sheets to the softening point of the glass, bending the heated sheets to a desired curvature and then cooling the bent sheets in a controlled manner to a temperature below the annealing range of the glass. During such treatment, a glass sheet is conveyed along a substantially horizontal path that extends through a tunnel-type furnace where the glass sheet is one of a series of sheets that are heated to the deformation temperature of glass and along an extension of the path into a bending station where each glass sheet in turn is transferred onto a lifting mold that lifts the glass sheet into adjacency to a vacuum mold. Suction is applied to the vacuum mold to lift and hold the shaped glass sheet in pressurized engagement thereagainst. The lifting mold retracts to below the substantially horizontal path. At about the same time, a ring-like member having an outline shape conforming to that of the glass sheet slightly inboard of its perimeter moves upstream into a position below the upper vacuum mold and above the lower lifting mold. Release of the vacuum deposits the bent glass sheet onto the ring-like member. The ring-like member conveys the glass sheet into a cooling station for rapid cooling. A transfer device removes the bent, tempered glass sheet from the ring-like member and transfers the removed sheet onto a downstream conveyor.
It would be beneficial for the glass sheet bending art to develop a type of transfer device that operates rapidly enough to minimize any bottleneck in the fabrication of sharply bent, tempered glass sheets. It would also be beneficial to have a transfer device that does not distort a bent, tempered glass sheet in order to impart a more precise shape to the thinner glass sheets presently treated for the production of tempered side windows and rear windows of automobiles and other vehicles. It would also be beneficial to have a transfer device that does not scratch the glass surface or scrape it against nozzles in the cooling station when it transfers a bent, tempered glass sheet from a ring-like member to a downstream conveyor. Finally, it would be beneficial to have a transfer device that does not cause a transferred glass sheet to crash abruptly during its transfer so as to reduce and possibly even eliminate breakage of bent, tempered glass sheets during their transfer.
Glass sheets have also been bent and tempered by mounting a flat glass sheet in bending relation to an outline mold of ring-like configuration, supporting the glass sheet on the mold while conveying the mold through a tunnel-type furnace where the glass sheet is heated to above its deformation point so that it sags by gravity to conform to the shape of the mold in both elevation and outline. If desired, the shape of the glass sheet conforms to a complicated shape by temporarily removing the sheet from the outline mold to impart a complicated shape by press bending, for example, before replacing the bent glass sheet onto the outline mold. The mold with its supported bent glass sheet immediately transfers to a cooling station where the glass sheet cools at a sufficiently rapid rate to impart at least a partial temper in the glass. In the past, the bent, tempered glass sheet was supported on the outline mold for further cooling to handling temperature.
This system required a large number of outline molds for a mass production bending and tempering operation. A suitable glass sheet transfer device at a location where the bent glass sheet is tempered and its surface fully hardened would transfer the glass from the mold to an unloading conveyor at a temperature above the handling temperature and would reduce the number of outline molds needed for a mass production operation.